This information is particularly timely and important because many areas hard hit this week don't usually see this amount of snow and ice
Tampa, FL (Vocus) March 2, 2009
The Institute for Business & Home Safety (IBHS) is offering guidance to help home and business owners protect their property from severe winter weather, including roof collapse from the weight of heavy snow and water damage due to ice dams.
"This information is particularly timely and important because many areas hard hit this week don't usually see this amount of snow and ice," said IBHS Chief Engineer Tim Reinhold.
Snow load risk depends in large part on the age of the building, although design loads have not changed much in recent years. Buildings with light weight roofs, such as metal buildings, will typically have less capacity to handle a high snow load. For flat roofs, the step-down area between roof sections is a potential problem because of the tendency for ice and snow collection.
The best source for determining how much snow load a building can handle is the design plan. IBHS says most roof designs can handle at least 20 lbs per square foot. Design loads can range from 10 to 20 lbs per square foot in Mid-Atlantic states and between 40 and 70 lbs per square foot in New England. IBHS offers these general guidelines to help estimate the weight of snow:
- Fresh snow: 10-12 inches of new snow is equal to one inch of water, or about 5 lbs per square foot of roof space, so you could have 4 feet of new snow before you need to worry. However wet snow can weigh considerably more and rain on top of snow can create problem if it doesn't drain from the roof.
- Packed snow: 3-5 inches of old snow is equal to one inch of water, or about 5 lbs per square foot of roof space, so anything more than 2 feet of old snow could be dangerous.
- Ice: if there's ice, it's much heavier, with one inch equaling about a foot of fresh snow.
For safe removal that won't endanger you or damage your roof, consult a roofing contractor.
To help minimize the risks from melting snow, IBHS suggests keeping attics well ventilated to reduce the risk of ice dams forming. A warm attic melts snow on the roof, causing water to run down and refreeze at the roof's edge where it's cooler. An ice buildup blocks water from draining and forces water under the roof covering and into the attic or down the inside walls.
Commercial buildings with flat roofs are particularly vulnerable to roof overload and leaks if ice dams clog roof drains. Water can also find its way inside on sloped roofs along the eaves.
To maintain proper drainage, remove snow from window wells and all walls. Clear debris from basement drains. Make sure gutters are clean and stable to ensure proper drainage.
For more information visit the IBHS Web site http://www.DisasterSafety.org.
IBHS is an independent, nonprofit, scientific and educational organization supported by the property insurance industry. The organization works to reduce the social and economic effects of natural disasters and other risks to residential and commercial property by conducting research and advocating improved construction, maintenance and preparation practices.